A stop and blow is when you pull off the road or park somewhere to either:

A)Roll up a blunt and continue driving or
B)Straight up park and take a hit.

Derived from Stop and Go, which is a stop for gas or some shit.

Guy 1: What's with those guys at the far end of the parking lot just sitting there?
*Windows roll down, smoke fumes out, car drives away slowly*
Guy 2: I see, just a little stop and blow. I will call the authorities.